Can you explain in more detail? It wasn't clear to me how this problem was handled. I did a little research and learned that the fast neutrons cause neutron activation, creating often long-lived radioactive isotopes of what they hit - which will generally be the reactor containment walls.
He did mention breeding tritium via lithium, so is the idea to plate the inner walls of the reactor with lithium? In that case, does the amount of tritium generated balance with the amount consumed? Or, does that just naturally reach equilibrium?
In any case, I think all of this is only alluded to in the video. If you have more insight, I think it would be useful to share it.